This invention relates to apparatus, systems and methods for converting energy present in ocean surface waves into electric energy.
A known wave energy converter (WEC) system for capturing ocean wave energy and converting it to electrical energy includes: (a) a first structure (which may be referred to as a “shell” or “vessel” or “float”) which, when placed in a body of water, is designed to move up and down, generally, in phase with the waves in the water and thus absorb and/or release energy; (b) a second structure (which may be referred to as a “shaft”, “spar”, “column” or piston) which is either stationary (e.g., tethered) or moves generally out of phase relative to the waves and the first structure; and (c) a power take off (PTO) device coupled between the first and second structures and which in response to the relative motion between the first and second structures is designed to produce electrical energy.
To avoid problems associated with mechanical and hydraulic PTOs, it has been suggested to use a linear electric generator (LEG) for a power take-off (PTO) device. However, a significant problem with extracting power efficiently from a wave energy converter (WEC) is the fact that wave motion is of relatively slow speed and, consequently, the relative movement between the column and shell is correspondingly slow. Thus, by way of example, where a linear electric generator (LEG) is used as the PTO, there is generated alternating current (AC) voltages which tend to be of low amplitude and low frequency. Processing and or rectifying low amplitude AC voltages tends to be inefficient because of the fixed losses in the rectifying networks; i.e., approximately 1 volt to 1.5 volts are normally lost across the rectifying networks. Processing low frequency signals is generally inefficient in that it requires the use of physically large inductors, transformers and capacitors. This also tends to increase the costs of the system and to decrease its efficiency.
It is therefore desirable to have apparatus which can produce AC voltages of higher amplitude and higher frequency